FR2591015A1 - WRITING METHOD WITH UPDATING AND READING INFORMATION ON A NON-ERASABLE MEDIUM ORGANIZED IN AREAS - Google Patents

Abstract

Method of writing with updating and reading of information on a non-erasable medium organized in sectors. Each sector includes a SYNC synchronization field, a CD data field, a CL length field, a CT type field, a CA address field and a CR redundancy field. The data information to be stored and its length are entered respectively in the CD and CL fields. The value entered in the CT type field indicates whether or not the data information can be updated. If the update is possible, the address field CA receives a pointer designating a free sector of the medium, this sector thus being reserved for a possible update. If the update is not possible, a predetermined value is entered in the CA address field. The error correction code entered in the redundancy field takes into account the contents of the CD, CL, CT and CA fields. Registration in all the fields of a sector is done in a single write operation. (CF DRAWING IN BOPI)

Description

WRITING METHOD WITH UPDATE AND READING

  INFORMATION ON A NON-ERASABLE MEDIUM

ORGANIZED BY SECTORS

  The subject of the present invention is a process

  writing dice with updating and reading information

  mations on a non-erasable support organized in sec-

  teurs. Non-erasable media are used in

  particularly for the archiving of voluminous information

  because they are inexpensive. These media tend to be used more and more in applications

  archiving of scanned files and documents.

  The digital optical disc is a

  example of non-erasable support organized into sectors.

  On such a support, it is possible to write an in-

  training at any time, on any sector, but it is no longer possible to modify this sector afterwards. Such a medium is said to be of "WORM" type (for "Write Once Read Many", that is to say single writing multiple reading). These "WORM" type supports are

  very well suited for archiving data that does not

  not read. However, even in applications

  archiving, it is necessary to keep certain

  information, such as lists or indexes

  allowing access to archived data.

  A commonly accepted solution consists in associating with the non-erasable support an erasable support

  in which the information which can

  wind evolve. This solution has two drawbacks.

  major customers. First, the loss of information

  erasable media may prevent

  dear any access to the information contained in the

  non-erasable support; this is the case when the sup-

  erasable port contains lists or indexes

  putting access to archived data. Secondly, since the non-erasable support cannot function, the non-erasable support can only function with the information contained in the erasable support, these two supports must be permanently associated, for example during transport or storage.

  There are also known methods for

  both updating information on the non-erasable disc itself. A first method of this type is described in European patent application EP-A1-O 046 323. The main objective of the method

  writing and reading subject to this de-

  patent application is the making of a registration

  without error on a non-erased information medium

  ble organized into sectors. This method consists of writing information in a sector and re-reading this information immediately after writing for verification purposes. An address vector is then added to the information which must be written in the following sector, this address vector thus indicating

  that the previously registered sector contains an in-

  correct training. This address vector allows, at the

  proofreading, to transfer to the user only the information

  training written correctly. The problem of updating the stored information is also raised

  (page 3, line 26 - page 4, line 22).

  The method described makes it possible to update small amounts of information, such as pointers. However, this method has two important shortcomings, which are, firstly, that the information

  news is recorded at the expense of the correct code

  error, which can quickly lead to making the entire sector unusable, and that on the other hand, this method can only be carried out at the level of the non-erasable support control unit,

  that is to say by the manufacturer Himself.

  Another method of updating information

  mation on a non-erasable support is described in the article "Dynamic data structures on optical disc" by

  Peter RATHMANN published in Proceedings of the Interna-

  tional Conference on Data Engineering, Los Angeles,

  April 24-27, 1984, pages 175 to 180. An early method

  defined by the author consists in associating with each survey

  one or more pointers. When the information

  initial mation is registered in a sector, the

  associated pointers are left blank. When he has-

  just necessary to update the information

  naked in the sector, the new information is ins-

  crite in a new sector and the sector pointer

  tor containing obsolete information is loaded with a value indicating the address of the sector containing the

  new information, and the pointer to the associated sector

  cie to the new information is left blank. The

  same operation is repeated for successive updates

  discontinuous, we thus obtain a linked list of sec-

  ters whose last sector contains information

the most recent.

  The author points out that the most important difficulty in this method is the fact of providing an update pointer. Indeed, non-erasable media such as optical discs are designed for archiving important files and are ill-equipped for writing small amounts of

  data anywhere in an area, operating

  tion which is necessary to update the poin-

  tor. Another problem stems from the difficulty of

  achieve precise positioning of the writing head

  re. Finally, writing small amounts of data is not very effective because it tends to reduce the error correction capacity in Information

written in the sector.

  The invention aims to remedy the drawbacks of known methods of updating

  information on a non-erasable medium. The process

  The purpose of the invention is in particular to allow the recording of any number of modifications.

  successive tions, without degrading the information.

  The process of the invention consists in adding

  ter, to the data information to be stored, a

  chaining information to logically link a

  appears to be sectors containing data information

  initial births and its various successive updates

  stops. In this process, the sector is considered to be an indivisible entity for write and read operations. The information allowing the chaining of the sectors is written at the same time as the data information, which

  eliminates the difficulties indicated in the

  ticle, already cited, entitled "dynamic data structure on optical disc" due to the fact that the write operation

  of a pointer in a sector is dissociated from the ope

  writing ration of data information in this sector. In the method of the invention, the pointer contained in the chaining zone is registered, together with the data information of the sector, with an address value designating a free sector, which

  may be used for updating the information

  tion of data. However, in order not to waste space on the non-erasable medium, no free sector is reserved in the case where the data information contained in a sector is declared non-modifiable. Specifically, the subject of the request is a method of writing information on a non-erasable medium organized into sectors, each sector comprising at least one synchronization field, one data field, one length field, one field. address and a redundancy field, method in which a synchronization code is entered in the synchronization field, data information

  in the data field and the length of said in-

  forming data in the length field, said method being characterized in that a type field is also provided in which a type code is entered to indicate whether the data information is fixed or can be updated, in that an address code is entered in the address field to designate a free sector if said data information can be updated, said free sector being thus

  reserved for possible updating of information

  tion of data, and a predetermined value in the address field if said data information is fixed, the writing in all the fields of the sector being made by a single writing operation, the redundancy code written in the field of redundancy taking into account at least the contents of the fields of

  data, length, type and address.

  By redundancy field is meant that a space is reserved in each sector for storing one or more redundancy bits. It should be remembered, and this is well known to those skilled in the art, that these

  redundancy bits are not necessarily consecu-

  tifs on the sector but that they can be distributed

  over the entire length of the sector, in particular by

  lacing with data from the other fields of the sec-

  tor. This is the case for example when the bits of

  redundancy are produced by a Hamming code applied

  qué to the data corresponding to the concatenation of the information of the fields of data, length,

type and address.

  Preferably, the type code indicated

  as data information can be changed

  is taken from a predetermined set of codes

  taking at least the following codes: - start, which indicates that the sector contains an in-

  initial data formation, i.e. not modified

  trusted, - addition, which indicates that the information contained in the current sector must be added to that of the previous sector, the latter being the one whose address code designates said current sector, - replaces, which indicates that the information contained in the current sector must replace that of the previous sector, the latter being the one whose

  address code designates said current sector.

  The subject of the invention is also a process

  Reading die for Restitution of information

  stored on the non-erasable support.

  The characteristics and advantages of the

  vention will emerge better from the description which goes

  follow, given by way of illustration but not limitation, with reference to the appended drawings, in which: - Figure 1 illustrates the division of a sector of the non-erasable support into several fields of information, the recording of information in the different fields of the same sector being done, according to

  the process of the invention, during the same operation

writing tion,

  - Figure 2 illustrates the chaining of sec-

  teurs containing successive updates of the same initial information,

  - Figure 3 is a flowchart of the different

  annuity steps of the writing method of the invention, and

  - Figure 4 is a flowchart of the different

  annuity steps of the reading method according to the invention.

  Figure 1 shows the different information

  which are registered in a sector S of the support

  not erasable, assuming the redundancy bits

  dance are consecutive. A similar figure could be established, when the redundancy bits are interleaved with at least some other data -from

  sector. In this first hypothesis, the informa-

  tioris memorized at the head of sector S are information

  SYNC synchronization to allow the

  1 read-write head of the media control means

  non-erasable port to position itself correctly at the start of the sector for a read operation. Sector S also includes a CD data field,

  a chaining field CC and a redundancy field CR.

  The respective lengths of these information fields

  are denoted LD, LC and LR. The redundancy field re-

  has a classic error correction code that holds

  account of the data contained in the data fields

born and chaining.

  Whatever the distribution of the redundancy bits in the sector, the chaining field CC is itself broken down into three information fields: an address field CA, a field of type CT and a field of length CL. These different fields have respective lengths LCA, LCT and LCL. The CA address field contains a pointer to designate another sector of the non-erasable medium. This other sector is used

  when it is necessary to update the information

  tion contained in the CD data field of sector S. The CT type field is used to indicate, if the data information contained in the CD data field is likely to be updated. This data field can therefore contain at least two

  values, one indicating that the data information

  data stored in the CD data field cannot be modified, the other indicating that this data

can be changed.

  Although not strictly necessary

  It may be advantageous to provide different type codes depending on whether the data information contained in the sector S is initial information,

  or a subsequent update of an information

  tial. In some applications, the operation of

  update can only consist of replacing it

  out of date information. A unique type code

  indicating the update is then sufficient. In re-

  vanche, in some other applications, the update can correspond as well to the replacement of

  obsolete information, or adding information

  tion which completes the initial information. In

  in this case, two update type codes are required

saires.

  The last information field of a sec-

  tor S is the length field CL. This field contains a value indicating the length of the information of

  data stored in the CD field.

  For example, for a sector S having

  a length of 1024 bytes (not including information

  synchronization and redundancy), the long

  LD length of the CD data field and LC length of the

  CC chaining field can be equal respectively-

  lie at 1020 bytes and 4 bytes. These 4 bytes, or 32 bits, can for example be distributed as follows: 20 bits for the address field, or 220 possible sector addresses, 10 bits for the field of length CL or 210 bytes, which corresponds to the maximum length of information contained in the

  CD data field, and 2 bits for the type field.

  These two bits represent 4 values

  corresponding to 4 types of sector: a sector containing

  providing initial information that can be changed, a sector containing information to be added to a

  previous information, a sector containing an in-

  training to replace previous information

  superior, and a sector containing information that does not

can be changed.

  FIG. 2 shows a possible state of a non-erasable medium in which information D1,

  D2 and D3 were initially memorized, the information

  D1 and D3 data having been subsequently updated. The non-erasable support consists of a consecutive series of sectors. In the case of a digital optical disc, this series of sectors

  forms a spiral path on the surface of the disc.

  Originally, all sectors are free.

  During the first write operation on the media

  non-erasable port, data information to me-

  moriser are listed in the order of sectors li-

  increasing indices. So in the example of the

  Figure 2, the sectors S1, S2, S3 respectively receive

  D1, D2 and D3 data information. The ins-

  the writing of data information in a sector is accompanied, during the same writing operation, by writing the length of this data information in the length field CL of said sector, of the type of this information in the CT type field of said sector and the entry of a pointer in

  the CA address field of said sector.

  Data information entered in a sector, during the first write operation

  on the non-erasable support, can be information

  tion likely to be updated or information that cannot be changed. The type T code provides information on the nature of the sector. For example, sectors S1

  and S3 in FIG. 2 contain information above

  capable of being updated while sector S2 contains information which cannot be modified. The type code "00" designates the second case and the code

of type "01" the first case.

  The pointer which is memorized in a sector is only useful if the information contained in this

  sector can be changed. This value is therefore in-

  different in the case where type T has the value "00". Any predetermined value can therefore be entered in the sector address field in this case. On the other hand, when the sector contains information which can be updated, the pointer is used to designate a free sector in which, if necessary, the update information can be stored. The designated free sector may simply be the first free sector in the sequence of

non-erasable support sectors.

  Consider the case where the data information

  born D1 contained in sector S1 becomes obsolete

  and should be replaced by other information.

  This modification of the information D1 is possible since the value of the type T of the sector S1 is equal to "01". Data information D intended to replace n

  D data information that has become obsolete is ins-

  written in sector S whose address is indicated n by the pointer contained in the CA address field of the

sector S1.

  The write operation on the sector S is n analogous to the write operation on the sector S1, that is to say that the values of all the fields of the sector are written simultaneously. The data fields CD and length CL receive respectively

  the information Dn and the length of this information.

  The address field CA receives a pointer designating a free sector of the non-erasable medium. Finally, the

1 1

  CT type field receives a value indicating that the

  Dn training replaces D1 information which has become obsolete-

  you. The value of this type code is for example "11".

  Replacement of data information

  born by another is a first possibility of update. Another possibility is to complete

  data information stored by another in-

  data formation, initial data information

  The being preserved. For example, as shown in

  in FIG. 2, data information Dp comes to include

  complete the data information Dn. The writing of the complementary data information D is done P in the sector S designated by the pointer contained p

  in the address field of sector S whose informa-

not

tion must be completed.

  The write operation in this sector S P is analogous to the write operation which consists in

  replace obsolete information, the only difference

  this residing in the value entered in the CT type field. In the case of updating by adding data information, the value of the code

  type is for example equal to "10".

  The number of successive modifications affecting initial data information, by replacement or addition, is only limited by the capacity of the non-erasable medium. In practice, the information that is stored on a medium that is not

  erasable are only called upon to undergo little modification

  cations over time, because otherwise there is no integration

  stop storing this information on a medium not

  erasable. It is therefore sufficient to provide one or two sec-

  free teachers for each sector containing information

  mation likely to be updated.

  We have described, with reference to FIG. 2, the

  different write operations that can be performed

  killed on the non-erasable support. The characteristics

  ques of these different writing operations, which constitute the writing method of the invention, will appear more clearly on reading FIG. 3 which represents a flow diagram of this writing method.

  This flowchart includes operating steps

  ration represented by a rectangle at an input and an output, and interrogation or test steps represented by a diamond at an input and at least two outputs, The different outputs corresponding to the different possible answers to the test. All of these steps are between a start step 2

and an end step 4.

  The operation steps are as follows:

  a) a step 4 of defining the information.

  tion of data D to be stored, of the length L of this data information and of the type T of the sector

  in which this data information will be stored

  laughed. This information is recorded in a memo.

  re buffer while waiting to be transferred to a sec-

  erase of the non-erasable support; b) an operation 8 of allocating a free sector S of the non-erasable support, and of writing in the data fields, of type and length of this sector of data information D, of type T and of

  length L. Any value is also ins-

  written in the address field of sector S; c) an operation 10 for allocating two free sectors S0 and S1, and for recording in the data, type, length and address fields of sector S0 data information D, of type T, of length L and address of sector S1; d) an operation 12 for initializing a loop index i to the value 1; e) an operation 14 for reading the content of a sector S. defined as being the i + 1st sector of a chain of sectors starting with a sector S0 of type "01"; f) an operation 16 for incrementing the loop index i, and

  g) an operation 18 for allocating a sec-

  tor free If +1, and writing in the data fields, type and length of a sector S. data information D, type T and length L, and writing in the field address of sector S. de

* the address of the free sector of the address S + 1.

  The flowchart also includes the following three tests: a) a test 20 on the value of the type T defined in operation step 6; b) a test 22 on the type of a sector S for which an update of the data information is requested; c) a test 24 on the state, free or not, of a

sector S ..

  In all cases, the writing process begins with the start step 2, followed by operation 6 consisting in defining the values to be entered in the

  data, length and type fields of a sec-

  tor. The process continues with test 20 which analyzes

  se is the value of type T. Three responses are possible which are either T = "00" (case of non-modifiable data information), or T = "01" (case of initial data information which can be updated day), either T = "10" or "11" (data information modifying a

  information already stored in a sector).

  In the first case (T = "00"), the process continues with the execution of operation 8. A single

  sector is allocated and it receives the defi-

nies in Operation 6.

  In the second case (T = "01"), test 20 is followed by operation 10. Two free sectors are allocated, the first to receive the information defined in operation 6, the second designated by the pointer registered in The address field of the first sector to allow a possible update of

  The data information contained in this first sec-

  tor. In the third case (T = "I'0" or "11"), the writing process successively comprises test 22, operation 12, operation 14, test 24, then operation 18 if the response to test 24 is positive, or operation 16 then again operation 14 and the

  test 24, if the answer to test 24 is negative.

  An update operation on an information

  mation of data contained in a sector of the non-erasable medium can be an operation of adding data information (T = "10") or an operation of replacing said data (T = "11"). In both

  In this case, the update operation relates to information

  tion of data contained in a sector of type T = "01". The object of test 22 is to check whether this condition is fulfilled. If not, a

  error code is issued and the information update

  data cannot be performed.

  If the sector to which the update request relates is indeed of type "01", it is necessary to reach the sector containing the most recent update by following the chaining between the initial sector and this last sector. This traversal of the chain of sectors is carried out by operations 12, 14 and 16 and test 24. It is recognized that a sector is the last in a chain when its successor, designated by the pointer contained in the address field of said sector, is a free sector. Operation 18 is then carried out to find another free sector S + 1 and to register in the sector If the data information, of type

  and length defined in operation 6.

  We will now describe, with reference to the flowchart of Figure 4, the reading process

  corresponding to the writing method of the invention.

  This flowchart includes a set of operations, each represented by a rectangle with one input and one output, and a set of tests, each represented by a diamond with one input and several outputs, each output corresponding to a particular response to the test. The flowchart also includes a start step 26 and an end step 28. The read operation relates to a sector S of the non-erasable support. The flowchart comprises the following operations: a) an operation 30 for reading the content of the sector S and assigning to a variable T the value of the type field of the sector S; b) two operations 32, 34 of assigning to a variable INF the value of the data field of sector S, and of assigning to a variable L the value of the length field of sector S; c) an operation 36 of assigning the sector S to a variable SO and of initialization to the value 1 of a loop variable i; d) an operation 38 for reading a sector S. equal to i + 1me sector of a chain of sectors i starting with a sector of type T = "01";

  e) an operation 40 for updating the information

  INF data formation by adding -information-

  tion contained in the data field of the sector Si, and updating the length L of the information INF by adding the value contained in the length field of the sector S .;

  f) an operation 42 for updating the INF information by eliminating the data information

  data contained in the data field of the sector Si1 and by adding the data information contained in the data field of the sector Si, and updating of

  The length L of this information INF by subtrac-

  tion of the value contained in the length field of the sector Si_1 and by adding the value contained in the length field of the sector Si; g) an operation 44 for incrementing

the loop index i.

  The flowchart also includes the following tests: a) a test 46 on the value of the variable T calculated in operation 30; b) a test 48 on the state, free or not, of sector S .; and * 1 c) a test 50 on the value contained in the type field of the sector Sil The read operation of a sector S depends on the value of the type field CT of this sector. This value is determined during operation 30. Test 46 on the value of the type field is then executed. If this value is "00", indicating that the sector S contains data information which cannot be modified, the read operation continues with operation 32; the data sought INF is contained in the data field CD of the sector S and its length L is equal to the value of the length field CL of the sector S. The read operation is terminated. In the case where the type field contains the value "01", indicating that the sector S contains initial data information which could have been updated later, Reading requires browsing

  The chain of sectors containing the successive updates

  stops. This Reading begins with operation 34 which assigns the data information contained in the data field of the sector S to a variable INF. This variable is stored in a working memory during the Read operation. Likewise, a variable L is defined to indicate the Data length of the variable INF. This variable Lest initialized with the value of the length field CL of the sector S. The next operation is operation 36

  initialization of two loop variables, a value

  riable S0 with sector S and a variable i with La

value 1.

  The successor S1 of the initial sector S0 is then determined by operation 38. The address of this successor is the value contained in the address field CA of the sector SO. Test 48 is applied to sector S1 to find out whether it is free or not. If sector S1 is free, it is because it constitutes the last sector of the chain of sectors starting with the

  SO sector; the reading is therefore finished. If the dry-

  sor S1 is not free, it is because it contains an in-

  data information update training

contained in the variable INF.

  This data information is normal-

  data information intended to replace (if type T has the value "11"), or to be added to (if type T has the value "10"), the information of

  data already read in the previous sectors and memo

  laughed at in the variable INF. The object of test 50 is precisely to determine the type T of sector S1. Values of type "00" and "01" are considered to be

errors.

  If the type of sector S1 has the value "10",

  the variables INF and L are updated by the operator

  ation 40. This is to add to the information

  of data already contained in the variable INF, the

  formation of data contained in the data field CD of sector S1, and to add to the value L the value

  of the length field CL of sector S1.

  If the type of the sector S1 has the value "11", the updating of the variables INF and L is carried out according to operation 42. This consists of deleting

  in the variable INF the corresponding data information

  corresponding to the data field CD of sector S0, anteces-

  tooth of S1, and to add the data information con-

  held in the CD data field of sector S1. The

  variable L is modified in the same direction.

  After updating the variables INF and L, the loop index i is incremented by operation 44 and the processing continues with operation 38 for the

next sector of the chain.

  The operation is repeated until the

  sector If read during operation 38 be a sec-

  free. The reading is then finished. The variable INF contains the data information sought; its length is equal to L.

Claims (3)

  1. Method of writing information on a non-erasable support organized into sectors, each   sector comprising at least one synchronization field   tion (SYNC), a data field (CD), a length field (CL), an address field (CA) and a redundancy field (CR), method in which a   synchronization code in the synchronization field   tion, data information in the data field   born and the length of said data information   in the length field, said method being characteristic   terized in that a type field is also provided   (CT) in which a type code is entered for indi-   quer if the data information is fixed or can be updated, by entering an address code in the address field to designate a free sector if said data information can be updated, said free sector being thus reserved for a possible update of the data information, and a predetermined value in the address field if said data information is fixed, the recording in all the fields of the sector being made by an operation single write, the redundancy code entered in the redundancy field taking into account   at least the contents of the data fields, of sender, type and address.   2. Method according to claim 1, charac-   terized in that the type code indicating that an in-   data formation can be updated is taken from a set of predetermined codes comprising at least the following codes: - start, which indicates that the sector is the first sector registered, - addition, which indicates that the information contained in   the current sector must be added to that of the sec-   previous author, the latter being the one whose address code designates said current sector, - replaces, which indicates that the information contained in the current sector must replace that of the previous sector, the latter being the one whose   address code designates said current sector.   3. Method according to any one of the res-   dications 1 and 2, characterized in that, for the restitution of stored data information, a first sector is read containing an initial data information, the type of said first is determined   sector, the information returned being equal to the   data formation of said sector if the type corresponds   pond to fixed data information, the information restored when the type corresponds to data information which can be updated being obtained in the following manner:   a) for each sector of the sec-   teurs starting with said first sector, the data information from said sector is extracted and the next sector is determined by the pointer of the address field of said sector, this operation being repeated until the next sector of a sector is a free sector,   b) the initial data information is modified   tial by the extracted data information,   each modification (addition or replacement) being de-   terminated by the type of sector from which the data information is extracted, the information restored   being equal to the initial information modified.